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Multiphoton absorption of entangled photons offers ways for obtaining unique information about chemical and biological processes. Measurements with entangled photons may enable sensing biological signatures with high selectivity and at very low light levels to protect against photodamage. In this paper, we present a theoretical and experimental study of the excitation wavelength dependence of the entangled two-photon absorption (ETPA) process in a molecular system, which provides insights into how entanglement affects molecular spectra. We demonstrate that the ETPA excitation spectrum can be different from that of classical TPA as well as that for one-photon resonant absorption (OPA) with photons of doubled frequency. These results are modeled by assuming the ETPA cross-section is governed by a two-photon excited state radiative linewidth rather than by electron-phonon interactions, and this leads to excitation spectra that match the observed results. Further, we find that the two-photon-allowed states with highest TPA and ETPA intensities have high electronic entanglements, with ETPA especially favoring states with the longest radiative lifetimes. These results provide concepts for the development of quantum light–based spectroscopy and microscopy that will lead to much higher efficiency of ETPA sensors and low-intensity detection schemes.
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This content will become publicly available on September 19, 2025
Impact of Classical and Quantum Light on Donor–Acceptor–Donor Molecules
Investigations of entangled and classical two-photon absorption have been carried out for six donor (D)-acceptor(A)-donor(D) compounds containing the dithieno pyrrole (DTP) unit as donor and acceptors with systematically varied electronic properties. Comparing ETPA (quantum) and TPA (classical) results reveals that the ETPA cross section decreases with increasing TPA cross section for molecules with highly off-resonant excited states for single photon excitation. Theory (TDDFT) results are in semiquantitative agreement with this anticorrelated behavior, due to the dependence of the ETPA cross section but not TPA on the two-photon excited state lifetime. The largest cross section is found for a DTP derivative that has a single photon excitation energy closest to resonance with half the two-photon excitation energy. These results are important to the possible use of quantum light for low intensity energy conversion applications.
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- Award ID(s):
- 2055565
- PAR ID:
- 10597705
- Publisher / Repository:
- J. Phys. Chem. Lett.
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry Letters
- Volume:
- 15
- Issue:
- 37
- ISSN:
- 1948-7185
- Page Range / eLocation ID:
- 9493 to 9501
- Subject(s) / Keyword(s):
- entangled photon, entangled two-photon absorption, time-dependent density-functional theory, donor-acceptor-donor
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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